In a wireless communications system such as a mobile cellular communications system, a wireless local area network (WLAN), or a fixed wireless access (FWA) system, communication nodes such as a base station (BS) or an access point (AP), a relay station (RS), and user equipment (UE) generally have a capability of transmitting their signals and receiving a signal from another communication node. Because attenuation of a radio signal in a radio channel is quite large, compared with a transmit signal of a local end, a signal from a communication peer end is quite weak when the signal reaches a receive end. For example, in a mobile cellular communications system, a difference of power between a receive signal and a transmit signal of a communication node reaches 80 dB to 140 dB or even larger. Therefore, to avoid self-interference imposed by a transmit signal on a receive signal of a same transceiver, transmitting and receiving of a radio signal generally use different frequency divisions or time divisions for differentiation. For example, in frequency division duplex (FDD), different frequency divisions separated by a particular guard band are used for receiving and transmitting to perform communication; in time division duplex (TDD), different time divisions separated by a particular guard interval are used for receiving and transmitting to perform communication. Both the guard band in the FDD system and the guard interval in the FDD system are used to ensure sufficient isolation between receiving and transmitting, and avoid interference imposed by transmitting on receiving.
Unlike an existing FDD or TDD technology, a wireless full-duplex technology can perform receiving and transmitting operations on a same radio channel at the same time; in this way, spectrum efficiency of the wireless full-duplex technology is theoretically two times of that of the FDD or TDD technology. Apparently, a precondition for implementing wireless full-duplex is avoiding, reducing, and canceling, as much as possible, strong interference (referred to as self-interference) imposed by a transmit signal on a receive signal, so that the self-interference does not affect correct receiving of a wanted signal.
In addition, to improve antenna utilization, a technology of receiving and transmitting via a same antenna is proposed.
When receiving and transmitting use a same antenna, a device such as a circulator is generally used to isolate a transmit end from a receive end. When a voltage standing wave ratio (VSWR) of the antenna is relatively small, for example, VSWR<1.2, receive and transmit isolation of 20 dB to 25 dB may be obtained by using the circulator.
When a channel bandwidth is relatively large (typically, when a bandwidth of a frequency band of 2 GHz to 3 GHz is greater than 10 MHz), an antenna impedance mismatch is relatively large, that is, a resistance component and a reactance component in the antenna impedance change with a frequency change, so that a VSWR change is relatively large. For example, on a frequency band of 2.4 GHz to 2.5 GHz, a VSWR of a wireless fidelity (WiFi) antenna generally changes within a range from 1.4 to 2.0. In this way, a self-interference signal that enters a receive end due to reflection by an antenna port is no longer a simple duplicate of a transmit signal with a different amplitude and delay (or phase), it is difficult to effectively cancel a self-interference signal component that enters the receive end due to reflection by the antenna port, and an effect of interference cancellation is severely affected.
Therefore, it is expected to provide a technology that can improve an effect of interference cancellation.